Waveguide junction circulator having resonant iris broadbanding plates



y 1970 T. A. HAGLER ETAL 3,519,958

WAVEGUIDE, JUNCTION CIRCULATOR HAVING RESONANT IRIS BROADB ANDIN GGGGG Es Filed NOV. 7, 1968 3 eets-Sheet 1 I/Vl 7'0 THO S 4. 6L W/L M 6. HEITH/JUS B) ATTORNEY July 7, 1970 T. A. HAGLER EPA!- WAVEGUIDE JUNCTION CIRCULATOR HAVING RESONANT IRIS BROADBANDING PLATES 3 Sheets-Sheet Filed Nov. '7, 1968 l xw 555cm: 8 Q3 Q3 0 3 w u Q4 Q4 4 Q moA i I :VLHH OHA o n MAC 5M AA X T E K rwy 34 n 7 3A B m 0N4 0N4 m 4 I 7 I 4 A @NA M531 P531 92 It; 25 52 :EE m2: I 25 Sort; 25 5%: 3) E 7 N 0 .n Sa o Q3 0 8 ATTORNEY July 7, 1970 T. A. HAGLER ETAL 3,519,958

WAVEGUIDE JUNCTION CIRCULATOR HAVING FESONANT IRIS BROADBANDING PL ATES Filed NOV. 7, 1968 3 Sheets-Sheet 5 2 o (n o 83 8 z 3 :0 3w

/ 16.8 FREQUENCY GH THOMAS A. HAGLE/P W/LL/AM C. HE/THAUS ATTORNEY FIG.3.

United States Patent 0 3,519,958 WAVEGUIDE JUNCTION CIRCULATOR HAVING RESONANT IRIS BROADBANDING PLATES Thomas A. Hagler and William C. Heithaus, Clcarwater,

Fla., assignors to Sperry Rand Corporation, a corporation of Delaware Filed Nov. 7, 1968, Ser. No. 774,162 Int. Cl. H011) 1/32, 5/12 US. Cl. 3331.1 4 Claims ABSTRACT OF THE DISCLOSURE An H-plane waveguide junction circulator-isolator characterized by increased bandwidth of impedance match between the circulator and the input and output waveguide transmission lines resulting from the use of a thin metal plate with a resonant iris opening connected across each said transmission line at the input and output arms of the circulator. The circulator is converted into an isolator by placing a load termination in the third arm of the circulator.

BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION In accordance with the present invention, an increase in the bandwidth of the impedance match between a waveguide junction circulator and the mating waveguide transmission lines at the circulator ports is achieved by providing a thin metal plate having a resonant iris opening connected across each waveguide transmission line at the respective circulator ports. Optimum match of the reactance slope of the iris with that of the circulator is achieved by choice of the proper iris opening aspect ratio and by making the iris resonant at a frequency below that of the unmatched circulator.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1a is a front elevation view, partly in cross-section, of a preferred circulator-isolator embodiment of the invention;

FIG. 1b is a top view of the embodiment of FIG. In;

FIG. 10 is a bottom view of the embodiment of FIG. la;

FIG. id is a side view of the embodiment of FIG. 1a;

FIG. 2 is a series of plots representing voltage standing wave ratio versus frequency characteristics typical of the embodiments of FIGS. la-ld.

FIG. 3 is a pair of plots representing insertion loss and isolation loss versus frequency characteristics typical of the embodiment of FIGS. la-ld.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the waveguide junction circulator-isolator embodiment of FIGS. 1a1d, a conventional H plane-T circulator is provided comprising rectangular waveguide 1, circulator waveguide 2, ferrite element 3, magnets 4 and 5 and respective pole pieces =6 and 7. The circulator is converted into an isolator by the addition of dielectric loaded,

3,519,958 Patented July 7, 1970 ice tunable, circular waveguide termination 8 which is inserted in the circular waveguide shunt arm 2 of the circulator. A similar circulator-isolator is described in the paper Tee Circulator by W. -E. Swanson and G. J. Wheeler in the 1958 IRE WESCON Convention Record, part I, pp. 151-156. The termination '8 comprises a tuning slug 9 and sleeve 10. The exposed surfaces of tuning slug 9 and sleeve 10 are coated with a conducting paint.

The voltage standing wave ratio versus frequency characteristic at input port 11 of the circulator-isolator comprising the elements represented by the numerals 1-10 is represented by dashed curve 11 of FIG. 2. A substantial increase in the frequency band over which the voltage standing wave ratio is minimized by the addition of thin metal plates 13 and 14, each having a resonant iris opening such as opening 20 in iris 14; the resulting VSW'R versus frequency characteristic at input port 11 is represented by solid line 15 of FIG. 2. The corresponding VSWR versus frequency characteristic at output port 12 of the circulator-isolator including the iris plates is represented by dashed line 16 of FIG. 2. Line 17 of FIG. 2 represents the VSWR versus frequency characteristic of the iris plate apart from the circulator-isolator. It will be observed that the iris plate is resonant at a frequency below that of the circulator-isolator without the iris plates.

A resonant iris aperture in a transverse partition within a waveguide manifests the characteristics of a shunt resonant circuit connected in parallel with the waveguide. It has been found that the reactive components of the admittance of a resonant iris aperture can be used to substantially cancel the reactive components of the admittance of an unmatched H-plane junction circulator by placing a resonant iris partition across the mating waveguide at each port of the circulator. The reactance slope of the iris is set for optimum match at the respective circulator port by properly selecting the iris opening aspect ratio and, hence, the iris Q. The iris opening may take various forms including rectangular, square, elliptical, circular and others with or without tuning posts or screws projecting into the opening.

It has been observed that optimum broadbanding results are achieved when the iris resonant frequency is appreciably below the resonant frequency of the unmatched circulator rather than at the same resonant frequency. This is the case with curves 11 and 17 of FIG. 2. It is thought that the interaction of the various closely spaced components comprising the waveguide junction circulatorisolator of the preferred embodiment makes the separation of the two resonant frequencies preferable.

The insertion loss and isolation characteristics of a typical design of the embodiment of FIGS. 1a-1d are given in FIG. 3, insertion loss being represented by curve 18 and isolation loss being represented by curve 19. It should be noted that the very significant increase in the operating bandwidth evidenced by a comparison of curves 11 and 15 of FIG. 2 is achieved by the addition of a simple element (thin metal plate having a resonant iris opening) of insignificant size and weight to an otherwise conventional waveguide junction circulator.

While the invention has been described in its preferred embodiment, it is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.

What is claimed is:

1. In an H-plane waveguide junction circulator having at least one each input port and output port,

said ports comprising rectangular waveguide transmission lines,

a pair of conductive plate means having resonant iris openings,

3,519,958 3 4 said his resonant frequency being substantially below References Cited the resonant frequency of the circulator in the 2113- UNITED STATES PATENTS sence of said conductive plates having resonant irises for the purpose of broadbanding said circulator, 3,311,849 7 Emma 333-1.1 each said plate means 'being placed across a respective 5 3,337,812 8/1967 Webbone of said waveguide transmission lines. 3,414,846 12/1968 CaSWell -11 X 2. The circulator defined in claim 1 wherein said input k and output waveguide ports are joined end to end to HERMAN KARL SAALBACH Pnmary Exammer form a continuous waveguide. P. L. GENSLER, Assistant Examiner 3. The eirculator defined in claim 2 and further having 10 a circulator waveguide shunt arm. US. Cl. XJR.

*4. The circulator defined in claim 3 wherein said shunt 333-24.2 arm is terminated with a load. 

